The present invention relates to a laser pulse stacking method for use, as an example, in an atomic vapor laser isotope separation (AVLIS) process.
An AVLIS process is an isotope enrichment process which involves the use of generation of laser beam pulses having a certain pulse repetition rate or frequency of operation (e.g., 5 KHz or higher) to photo-ionize an atomic vapor (typically uranium) to separate a particular isotope, such as U235, from other isotopes in the vapor.
The uranium enrichment process generally requires use of copper vapor laser beam pulses which desirably have the same temporal relationship between the center and outside edges of the beam cross-section.
A problem in the prior art has been the generation of such laser beam pulses where this temporal relationship is such that the outer edge of the pulse arrives sooner than the control core. This occurs because of the fact that the electrical skin effect of the laser discharge retards the laser excitation at the center of the beam, so that the resulting laser beam pulse is generated as an annular ring early in time. Later, the entire cross-section lases. Finally, only the core region lases, causing a radially shrinking pencil beam. This effect can have undesirable consequences, particularly where a series of laser pulses are desired to be in time synchronization, such as for use in an AVLIS process, as described above. A visualization of this effect yields a chevron shaped figure on a plot of beam radium versus time.